Mass spectrometers work by ionizing molecules and then sorting and identifying the molecules based on their mass-to-charge (m/z) ratios. Several different types of ion sources are available for mass spectrometers. Each ion source has particular advantages and disadvantages for different types of molecules to be analyzed.
Much of the advancement in liquid chromatography (LC/MS) over the last ten years has been in the development of ion sources. The introduction of techniques that are performed at atmospheric pressure have been of particular interest. These techniques do not require the use of complex pumps and pumping techniques to create a vacuum. Common techniques include and are not limited to electrospray ionization (ESI), atmospheric pressure chemical ionization (APCI), and atmospheric pressure photoionization (APPI).
ESI is the oldest and most studied of the above-mentioned techniques. Electrospray ionization works by a technique that relies in part on chemistry of the molecules to generate analyte ions in solution before the analyte reaches the mass spectrometer. The liquid eluent is sprayed into a chamber at atmospheric pressure. The analyte ions are then spatially and electrostatically separated from neutral molecules.
More recently, there has been a trend toward developing ion sources that use low flow rates and sample amounts. Nanospray devices work by being able to emit small amounts of analyte at low flow rates. At such flow rates the properties effecting molecules are different from standard electrospray techniques. However, at low flow rates and with analyte at very low levels it is often difficult to detect certain ions. It would, therefore, be desirable to provide an apparatus that can detect various ions at very low levels with increased sensitivity. These and other problems have been overcome by the present invention.